Swellable polymer with anionic sites

ABSTRACT

The invention is directed to stable crosslinked water-soluble swellable polymers and methods for making same. More particularly, the invention relates to a composition comprising expandable polymeric particles having anionic sites and labile crosslinkers and stable crosslinkers, said particle mixed with a fluid and a cationic crosslinker that is capable of further crosslinking the particle on degradation of the labile crosslinker and exposure of the anionic sites so as to form a gel. A particularly important use is as an injection fluid in petroleum production, where the expandable polymeric particles are injected into target zone and when the heat and/or suitable pH of the target zone cause degradation of the labile crosslinker and the particle expands, the cationic crosslinker crosslinks the polymer to form a gel, thus diverting water to lower permeability regions and improving oil recovery.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. nonprovisional application Ser.No. 12/797,402, filed Jun. 9, 2010, which claims priority to U.S.Provisional Application No. 61/185626 filed Jun. 10, 2009. Bothapplications are incorporated herein by reference in their entirety.

FEDERALLY SPONSORED RESEARCH STATEMENT

Not applicable.

REFERENCE TO MICROFICHE APPENDIX

Not applicable.

FIELD OF THE DISCLOSURE

The disclosure relates to crosslinked swellable polymers containinganionic sites that after swelling can be further crosslinked in situwith cationic crosslinkers, such as polyvalent metal cations or cationicpolymers, and methods for making same. A particularly important use isas fluid diversion agents for sweep improvement in enhanced oil recoveryapplications and also as drilling fluids in petroleum production, butapplications can also include uses in the hygiene and medical arts,packaging, agriculture, the cable industry, information technology, inthe food industry, papermaking, use as flocculation aids, and the like.

BACKGROUND OF THE DISCLOSURE

A “smart gel” is a material that gels in response to a specific physicalproperty. For example, it may gel at a specific temperature or pressure.Although finding many industrial uses, our interest in smart gels liesin their uses in oil and gas production, and in particular as adiverting agent to improve oil recovery from reservoirs.

The water injection method used in oil recovery is where water isinjected out into the reservoir to stimulate production. Water isinjected for two reasons: 1. For pressure support of the reservoir (alsoknown as voidage replacement). 2. To sweep or displace the oil from thereservoir, and push it towards an oil production well. Normally only 20%of the oil in a reservoir can be extracted, but water injectionincreases that percentage (known as the recovery factor) and maintainsthe production rate of a reservoir over a longer period of time.

However, sweep recovery is limited by the so-called “thief zones,”whereby water preferentially travels through the more permeable regionsof the reservoirs, bypassing less permeable zones, leaving unswept oilbehind. One means of further improving recovery is to block thief zoneswith a polymer or other material, thus forcing water through the lesspermeable regions.

U.S. Pat. No. 6,454,003, U.S. Pat. No. 6,984,705 and U.S. Pat. No.7,300,973 describe what might be called a “smart polymer” since itsproperties change in response to particular stimuli. These patentsdescribe an expandable crosslinked polymeric particle having an averageparticle diameter of about 0.05 to 10 microns. The particle is highlycrosslinked with two crosslinkers, one that is stable and a second thatis labile. The excess crosslinking makes the initial particles quitesmall, allowing efficient propagation through the pores of a reservoir.On heating to reservoir temperature and/or at a predetermined pH orother stimuli, the reversible (labile) internal crosslinks break,allowing the particle to further expand by absorbing additionalinjection fluid, usually water. The initial polymeric particle issometimes called the “kernel” before its expansion, in analogy to theway a kernel of popcorn “pops” in response to certain stimuli, such asheat.

The unique properties of this particle allows it to fill the highpermeability zones—commonly called thief zones or streaks—and then beexpanded so that the swollen particle blocks the thief zones andsubsequent injections of fluid are forced to enter the remainder of thereservoir, more effectively sweeping the reservoir. However, the methodis limited in practice because subsequent water injections always removesome of the polymer, thus the thief zones become washed out and againtransport most of the injection water limiting the injection fluidentering the less permeable zones.

The reason for the washout is not certain, but our own research suggeststhat the swollen polymer is not in gel form, thus although viscous, is aliquid and can be washed out of the porous substrate.

What is needed in the art is a “smart gel” that is less susceptible toloss under the conditions of use. In particular, a swellable polymerthat is resistant to wash out by subsequent fluid injections is needed,but the polymers will have utility in any application where swellablepolymers are desired.

SUMMARY OF THE DISCLOSURE

The disclosure generally relates to smart gels that have stable andlabile crosslinkers, allowing swelling in situ in response to aparticular stimuli. Further, the swelled polymeric particles containanionic sites that become accessible on swelling of the polymer and canthen be further crosslinked using cationic crosslinkers, such aspolyvalent metal crosslinkers or cationic polymers to produce gels.

Some of the more common inorganic crosslinking agents include cations ofchromium, iron, vanadium, aluminates, borates, titanium, zirconium,aluminum, and their salts, chelates and complexes thereof. Complexed orchelated metal cations are preferred because they slow the rate ofgelation, as are nanoparticles that slowly release metal ions. Commonorganic cationic polymers include polyethyleneimine and thepolyquaternium polymers.

The anionic sites include the various acids such carboxylic, nitric,phosphoric, chromic, sulfuric, sulphonic, vinylogous carboxylic acidsand the like. Suitable polymers having anionic sites includebiopolysaccharides, cellulose ethers, and acrylamide-based polymers,with negatively charged monomers.

Preferably, the smart gels of the invention comprise a highlycrosslinked expandable polymeric particles having labile crosslinkersand stable crosslinkers, wherein at least one of the monomers that makesup the polymer or copolymer contains anionic sites. A suitable cationiccrosslinker is added to the particles after they are made or after thelabile crosslinker degrades or any time therebetween. In certainembodiments it may be possible to convert a nonionic polymer to ananionic polymer, but the incorporation of anionic monomers is preferredto ensure adequate dispersion of anionic sites and for ease of use.

In reservoir applications, the cationic crosslinker can be injectedafter swelling of the polymer, but it can also be combined with theunexpanded particle in the initial injection fluid, and if necessary forthe application, the rate of gelation can be delayed by means known inthe art in order to allow the particle to fully swell before commencingthe gelation. In yet another embodiment, anionic particles and a secondpopulation of cationic crosslinker loaded particles can be combined andused.

The polymer of the invention has particular use in oil recovery, asdescribed above, and is preferably a hydrophilic polymer for thisapplication. However, such polymers would find uses in all of the artswhere swellable polymers are in current use and loss is not desired,including as filler for diapers and other hygiene products, medicaldevices such as orthopedic insoles, ocular devices, and biomimeticimplants, wipe and spill control agents, wire and cable water-blockingagents, ice shipping packs, controlled drug release, agricultural uses(e.g., soil additive to conserve water, plant root coating to increasewater availability, and seed coating to increase germination rates),industrial thickeners, specialty packaging, tack reduction for naturalrubber, fine coal dewatering, and the like.

By “polymer” what is meant is polymerized monomers, including mixturesof two or more monomers.

A “stable crosslinker” is defined herein to be any crosslinker that isnot degraded under the stimuli that causes the labile crosslinker todisintegrate. Representative non-labile crosslinkers include methylenebisacrylamide, diallylamine, triallylamine, divinyl sulfone,diethyleneglycol diallyl ether, and the like and combinations thereof. Apreferred non-labile crosslinking monomer is methylene bisacrylamide.

The “labile crosslinker” is defined herein to be any crosslinker thatdecays or is reversible on application of a particular stimulus, such asirradiation, suitable pH, temperature, etc. and combinations thereof.Representative labile crosslinkers include acrylate or methacrylateesters of di, tri, tetra hydroxy compounds including ethyleneglycoldiacrylate, polyethyleneglycol diacrylate, trimethylopropanetrimethacrylate, ethoxylated trimethylol triacrylate, ethoxylatedpentaerythritol tetracrylate, and the like; divinyl or diallyl compoundsseparated by an azo such as the diallylamide of 2,2′-Azobis(isbutyricacid) and the vinyl or allyl esters of di or tri functional acids, andcombinations thereof. Preferred labile crosslinking monomers includewater soluble diacrylates such as polyethylene glycol (PEG) 200-1000diacrylate, especially PEG 200 diacrylate and PEG 400 diacrylate, andpolyfunctional vinyl derivatives of a polyalcohol such as ethoxylated(9-20) trimethylol triacrylate and polymethyleneglycol diacrylate.

US 2008075667, herein incorporated by reference, describes additionalacid labile ketal cross linkers that can be used in the invention. Suchacid labile ketal crosslinker have one of the following formulas:

wherein Y is a lower alkyl, n and m are independently an integer ofbetween 1 and 10 and R1 and R2 are independently a lower alkyl.

In particular, 2-bis[2,2′-di(N-vinylformamido)ethoxy]propane (BDEP) and2-(N-vinylformamido)ethyl ether (NVFEE) are described and may besuitable in acidic environments, or where the acid is later addedthereto. Such cross linkers can be advantageously combined with themonomers described therein, such as N-vinyl pyrollidone, N-vinylformamide, N-vinylacetamide, N-vinylacetamine and other vinyl containingpolymers and copolymers thereof, and may be preferred where theneurotoxic effects of acrylamide are to be avoided.

“Cationic crosslinkers” are defined herein to be molecules that cancrosslink the anionic polymers, and include cationic polymers andpolyvalent metals, chelated polyvalent metals, and compounds orcomplexes capable of yielding polyvalent metals.

By “complex” or “complexed” what is meant is that the polyvalent metalcrosslinker is present with or within another molecule that will releasethe metal ions under the conditions of use, and includes the use ofmetal salts, chelates, nanoparticles, and the like.

The proportion of stable to labile crosslinker can also vary dependingon how much swelling on stimulus is required, but in the enhanced oilrecovery applications a great deal of swelling is desired to effectivelyblock the thief zones and increase the mobilization and/or recovery rateof hydrocarbon fluids present in the formations. Thus, the concentrationof labile crosslinker greatly exceeds the concentration of stablecrosslinker. To obtain sizes in the range of about 0.05 to about 10microns suitable for injection fluid use the crosslinker content isabout 1,000-200,000 ppm of labile crosslinker and from greater than 0 to300 ppm of non-labile crosslinkers.

Combinations of multiple stable and labile crosslinkers can also beemployed advantageously. Reaction to stimuli can also be controlled bylabile crosslinker selection, as needed for particular reservoirconditions or for the application at issue. For example, judiciousselection of labile crosslinkers—one that degrades at a very hightemperature and another at a lower temperature—can affect thetemperature and pH at which the kernel pops.

Other crosslinkers include, but are not limited to, diacrylyl tertiaryamides, diacrylylpiperazine, diallyltartardiamide (DATD),dihydroxyethylene-bis-acrylamide (DHEBA), and bis-acrylylcystamine(BAC), trimethylolpropane trimethacrylate (TMPTMA), propyleneglycoltriacrylate (PGTA), tripropyleneglycol diacrylate (TPGDA), allylmethacrylate (AMA), triethyleneglycol dimethacrylate (TEGDMA),tetrahydrofurfuryl methacrylate (TFMA) and trimethylolpropanetriacrylate (TMPTA). Multifunctional crosslinkers include, but are notlimited to, pentaerythritol triacrylate, 1,5 pentane dioldimethacrylate, and pentaerythritol triallylether.

It is believed that the carboxylate and/or other anionic constituentsare the crosslinking sites in the polymer and that the polymer cannotgel if there are too few crosslinking sites in the polymer, i.e., lessthan about 1.0 mole percent based on the total number of monomericgroups in the polymer. U.S. Pat. No. 4,683,949 shows gelation rates fora number of different polymers and conditions and is incorporated hereinby reference.

The solvent of the gelation system is an aqueous liquid, such asdeionized water, potable water, fresh water, or brine having a totaldissolved solids concentration up to the solubility limit of the solidsin water. Inert fillers known in the art may also be added to thegelation system to reinforce the subsequent gel if desired or for use asproppants. Such fillers include crushed or naturally fine rock materialor glass beads, sand and the like.

Representative anionic monomers that can be used include the followingacids and their sodium, potassium and ammonium salts: acrylic acid,methacrylic acid, maleic acid, itaconic acid, 2-propenoic acid,2-methyl-2-propenoic acid, 2-acrylamido-2-methyl propane sulfonic acid,sulfopropyl acrylic acid and other water-soluble forms of these or otherpolymerizable carboxylic or sulphonic acids, sulphomethylatedacrylamide, allyl sulphonic acid, vinyl sulphonic acid, and the like.Preferred anionic monomers include sodium acrylates.

Representative nonionic monomers include acrylamide,N-isopropylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide,dimethylaminopropyl acrylamide, dimethylaminopropyl methacrylamide,acryloyl morpholine, hydroxyethyl acrylate, hydroxypropyl acrylate,hydroxyethyl methacrylate, hydroxypropyl methacrylate,dimethylaminoethylacrylate (DMAEA), dimethylaminoethyl methacrylate(DMAEM), maleic anhydride, N-vinyl pyrrolidone, vinyl acetate andN-vinyl formamide. Preferred nonionic monomers include acrylamide,N-methylacrylamide, N,N-dimethylacrylamide and methacrylamide.Acrylamide is more preferred. N-vinyl pyrollidone, N-vinyl formamide,N-vinylacetamide, N-vinylacetamine and copolymers may be preferred withthe acid labile ketal crosslinkers of US 2008075667.

Cationic and betaine monomers can be combined with the polymericparticles of the invention, but their use is not preferred as they wouldcompete for binding to the anionic sites. However, small amounts may beacceptable, provided the anionic sites predominate.

Representative swellable polymers also include polymers and copolymersof acrylamide and 2-acrylamido-2-methyl propane sulfonic acid (and itssodium salt), copolymers of acrylamide and sodium acrylate, terpolymersof acrylamide, 2-acrylamido-2-methyl propane sulfonic acid (and itssodium salt) and sodium acrylate and homopolymers of2-acrylamido-2-methyl propane sulfonic acid (and its sodium salts),poly(2-hydroxyethyl methacrylate), poly(2-hydroxypropyl methacrylate),poly(isobutylene-co-maleic acid), and the like.

The “polyvalent metal crosslinker” of the present invention is definedas a salt or a complex of a tri- or quatravalent metal cation whereinthe metal cation is capable of crosslinking a polymer having anionicsites. Exemplary polyvalent metal crosslinking agents useful in thepractice of the present invention are complexes or chelates of Al3⁺,Fe3³⁰, Cr3⁺, Ti4⁺, Sn4⁺, Zr4⁺ and the like. Preferred crosslinkingagents of the present invention contain Al3⁺, Zr4⁺ or Cr3⁺, and theiracetates, nitrates, phosphates, carbonates, tartrates, malonates,propionates, benzoates, or citrates thereof, and the like. Combinationsof cationic crosslinkers can also be used.

The polyvalent metal cations can be employed in the form of complexeswith an effective sequestering amount of one or more chelating orsequestering anions. Slow release nanoparticles and macroparticles canalso be employed. Chromium and zirconium are the preferred cations inhigh salinity brines including hard brine. High salinity brine containson the order of at least about 30,000 ppm total dissolved solids. Thus,the combination of the particular chelating or sequestering agent inconjunction with the preferred chromium(III) and Zr(IV) cations confershigh brine tolerance.

The cationic polymers of the invention include homopolymers of thefollowing:

dimethyldiallyl ammonium chloride, ethyleneimine, methacrylamido propyltrimethyl ammonium chloride, 2-methacryloyloxyethyl trimethyl ammoniummethosulfate and diquaternary ionene, and the like. A preferred cationiccrosslinker is polyethyleneimine (PEI), which has a high charge ratio.

The particles can be prepared by methods known in the art, including theinverse emulsion polymerization technique described in U.S. Pat. No.6,454,003, U.S. Pat. No. 6,729,402 and U.S. Pat. No. 6,984,705. Particlesuspensions are prepared by mixing the particles with injection fluid,or inverse suspensions of particles are inverted with a surfactantand/or sufficient shearing and additional injection fluid can be addedif needed.

In addition to the expandable polymeric particles having anionic sitesand both labile and stable crosslinkers and the cationic crosslinker,the aqueous solution may also contain other conventional additivesincluding chelating agents, pH adjusters, initiators and otherconventional additives, accelerators, retardants, surfactants,stabilizers, etc., as appropriate for the particular application.

The rate of gelation with the polymers can be controlled, as is known inthe art. Thus, temperature and pH can affect the rate of gelation, ascan the use of metal complexes or metal nanoparticles or other means toslow the rate of release of metal cations, as needed for a particularapplication. In addition, the gels can be destroyed with the use ofstrong oxidizing agents such as sodium hypochlorite.

In one embodiment, the invention is a composition comprising a fluid, acationic crosslinker and expandable polymeric particles having anionicsites and both labile and stable crosslinkers. In another embodiment,the invention is a composition comprising expandable polymeric particleshaving anionic sites and both labile and stable crosslinkers, saidparticle combined with a fluid and a cationic crosslinker that iscapable of crosslinking the anionic sites in the popped polymer andforming a gel that is resistant to washout.

In another embodiment, the invention is a composition comprising highlycrosslinked expandable polymeric particles having an unexpanded volumeaverage particle size diameter of from about 0.05 to about 10 micronsand a crosslinking agent content of from about 1,000 to about 200,000ppm of labile crosslinkers and from greater than 0 to about 300 ppm ofstable crosslinkers, combined with a cationic crosslinker and a fluid.

In another embodiment, the invention is a method of increasing therecovery of hydrocarbon fluids in a subterranean formation comprisinginjecting into the subterranean formation a composition comprising afluid, a cationic crosslinker, and a highly crosslinked expandablepolymeric particle having anionic sites, wherein polymeric particle hasan unexpanded volume average particle size diameter of 0.05-10 micronsand a crosslinker content of about 1,000-200,000 ppm of labilecrosslinker and greater than 0 to about 300 ppm of stable crosslinker,said polymeric particle has a smaller diameter than the pore throats ofthe subterranean formation, and said labile crosslinkers break under theconditions of temperature and suitable pH in the subterranean formationto allow the polymeric particle to expand, thus exposing the anionicsites so that said cationic crosslinker can react with the anionic sitesto form a gel.

In preferred embodiments, the polymeric particles can be a copolymer ofacrylamide and sodium acrylate, the stable crosslinker can be methylenebisacrylamide, and the labile crosslinker can be a polyethylene glycoldiacrylate. The cationic crosslinker is selected from polyethyleneimine,Al3⁺, Fe3⁺, Cr3⁺, Ti4⁺, Sn4⁺, or Zr4⁺.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention provides a novel polymer containing anionic sites thatswells on a stimuli and is then additionally treated with a cationiccrosslinker that acts to gel the polymer by providing additionalcrosslinking Such smart gels have particular utility in sweepingreservoirs, but many uses are possible.

Example 1: Prior Art

We ran a number of slim tube tests in which we injected about 1 porevolume of BRIGHTWATER® particles (NALCO®, copolymer of acrylamide andsodium AMPS crosslinked with methylene bis-acrylamide and PEGdiacrylate) into 40′ slim tubes packed with sand. The sand pack was thenheated (150-190° F.) to allow the polymer to pop. Afterwards, water wasinjected into the sand packs and the resistance to the flow of watermeasured. While the popped polymers initially exhibited good resistancefactors, this behavior appeared to washout with additional waterinjection. Typically within one pore volume of water injection theResidual Resistance Factor (RRF) dropped to a number about 1-2. Thisbehavior was observed with slim tubes which were packed with 6.7 Darcysand as well as 1 Darcy sand. Therefore, the treatment effect of porousmedia with these particles was only temporary.

Example 2: Invention

Since the prior art polymer is subject to washout, we propose that whencombined with suitable anionic sites and further crosslinked withpolyvalent metal cations or a cationic polymer, such as PEI, theresulting gel will remain resistant to washout! After the polymerreaches the target zone in the reservoir, the unstable internalcrosslinkers PEG-200 or PEG-400 diacrylates hydrolyze and the particlethen opens up (swells, pops). The addition of the cationic crosslinkersuch as Cr3⁺ or PEI will crosslink the expanded polymeric particles viathe anionic sites, and is predicted to result in gel that is much moreresistant to washout.

We injected a gelant mixture containing 0.5% anionic microparticles ofthe present invention along with crosslinker-loaded particles containing100 ppm Cr(III) and 1200 ppm PEI into a 30′ long slim tube (6 sections,5′ each) packed with 4.5 Darcy sand. The gelant was injected into thefirst 0.5 PV of the sandpack and then pushed slightly further into thetube with additional brine injection. The sandpack system was then shutin at 150° F. to allow the gelation to occur. Several ampoulescontaining the gelant mixture were also placed in the oven to monitorthe gelation progress. Brine was periodically injected into the sandpackand the resistance to the flow was measured. The flow resistancegradually increased over time, and eventually a persistent ultra-high(>2000) RRF value was achieved, indicating superiority of the inventionpolymer over prior art example.

The following references are incorporated by reference herein in theirentirety.

U.S. Pat. No. 6,454,003, U.S. Pat. No. 6,729,402 and U.S. Pat. No.6,984,705

U.S. Pat. No. 3,727,688

U.S. Pat. No. 4,068,714

U.S. Pat. No. 3,749,172

U.S. Pat. No. 4,683,949

US 2008075667

What is claimed is:
 1. A method of increasing the recovery ofhydrocarbon fluids from a subterranean formation comprising injectinginto the subterranean formation a composition comprising water, acationic crosslinker, and a highly crosslinked expandable hydrophilicpolymeric particle having anionic sites, wherein: i) said polymericparticle has an unexpanded volume average particle size diameter of0.05-10 microns and a crosslinker content of about 1,000-200,000 ppm oflabile crosslinker and greater than 0 to about 300 ppm of stablecrosslinker, ii) said polymeric particle has a smaller diameter than thepore throats of the subterranean formation, iii) said labilecrosslinkers break under the conditions of temperature and suitable pHin the subterranean formation to allow the polymeric particle to expand,and iv) said cationic crosslinker then reacts with said expanded polymerto form a gel.
 2. The method of claim 1, wherein the cationiccrosslinker is a complexed polyvalent cation and is injected into thesubterranean formation at the same time as the highly crosslinkedexpandable polymeric particle.
 3. The method of claim 1, wherein thecationic crosslinker is a polyvalent cation and is injected into thesubterranean formation after expansion of the polymeric particle.
 4. Themethod of claim 1, wherein the cationic crosslinker is PEI and iscombined with the highly crosslinked expandable hydrophilic polymericparticle prior to injection into the subterranean formation.
 5. Themethod of claim 1, wherein the cationic crosslinker is one of more ofthe following: PEI, Al³⁺, Fe³⁺, Cr³⁺, Ti⁴⁺, Sn⁴⁺, and Zr⁴⁺.